Vehicles which have a communication device may exchange messages with other road users and/or the road infrastructure. These messages may trigger a response on the part of a recipient of the message, for example active modification of vehicle functions and/or a change in the direction and/or speed of the recipient. It may therefore be necessary to protect a communication system, in particular a communication network between vehicles, from malfunction and/or tampering.
In car-to-X communication, a communication device for example of a vehicle is usually able not only to transmit messages originally generated by the communication device but additionally also to re-transmit received messages. The range of the received message may thereby be increased, for example. This method is also known as hopping. To protect the communication device and/or the car-to-X communication network, the communication device may perform a plausibility check of a received message before re-transmitting said message. A plausibility check of the message may for example compare an item of speed and/or position information contained in the message with a restricted speed or position range. Conventional car-to-X communication devices have the disadvantage that they usually discard a message which was originally transmitted by the communication device and which has been re-received thereby due to hopping. This conventional approach is practical, since the re-received message cannot contain any new information. The disadvantage is that no information relating to the messages emitted by the communication device can be available to the communication device.